The air conditioning systems for motor vehicles in the prior art have long since had various individual components, such as the condenser traditionally arranged at the front of the vehicle, the compressor connected to the vehicle's engine and actuated by it, the evaporator arranged in the passenger compartment, as well as hoses and connections. The air conditioning system conditions the air which is then taken into the passenger compartment. The compressor is usually driven by the engine of the vehicle by coupling mechanical energy to the compressor shaft. Radiator fans and blowers draw electric power from the onboard 12 V network.
The components of the system are usually delivered separately to the vehicle manufacturing plant and installed there. Due to the many components, various installation steps are necessary, which in turn involve a large number of connections and make the installation a costly process. The connections to be made during the installation process are furthermore potential leakage sites, which may be very time consuming and cost-intensive to repair. Furthermore, the filling of the air conditioning system with refrigerant occurs only after the installation of all components belonging to the refrigerant circuit. This further increases the installation expense during the vehicle assembly process.
Air conditioning systems of this kind with coolant/air heat exchangers, which draw their heating power from the coolant circuit of an efficient internal combustion engine of the vehicle drive train, can no longer achieve the temperature level needed for a comfortable heating of the passenger compartment at low outside temperatures, such as below −10° C. The same holds for systems in vehicles with hybrid drive system. For these vehicles, the use of auxiliary heating concepts is necessary.
Glycol/air heat pumps also utilize the coolant of the internal combustion engine, but as a heat source. In this case, heat is taken away from the coolant. Consequently, the internal combustion engine will be operated for a longer time at low temperatures, which has a negative impact on the exhaust gas emissions and the fuel consumption. Due to the intermittent operation of the internal combustion engine in hybrid vehicles, a sufficiently high coolant temperature is not achieved in the case of long trips. Consequently, the start/stop operation of the internal combustion engine is suspended at low outside temperatures. The internal combustion engine will not be shut off.
Furthermore, there is a trend toward complete electrification of the drive train, such as vehicles powered by batteries or fuel cells. In this case, the waste heat of the internal combustion engine is no longer a possible heat source for heating the air.
Furthermore, the amount of energy that can be stored in the battery of the vehicle is less than the amount of energy that can be stored in the form of liquid fuel in the fuel tank. Thus, the power required for the air conditioning of the passenger compartment of an electric vehicle is furthermore an important influence on the travel range of the vehicle.
German Pat. Appl. Pub. No. DE 10 2009 028 522 A1 specifies a compact air conditioning system with an evaporator unit, a condenser unit and a component unit, as well as a refrigerant circuit. The evaporation unit and the condenser unit each have air-flow heat exchangers arranged in a housing, as well as a fan. The refrigerant circuit, comprising an evaporator, a condenser, and a reheater, is configured for a combined refrigerator and heat pump operation, as well as a reheating mode, while in the reheating mode the heating power of the reheater, configured as a condenser/gas cooler, and the cooling power of the evaporator can be regulated independently of each other. The operating modes of the air conditioning system are controlled by the refrigerant circuit. Thus, the air conditioning system fulfills the function of a heat pump, which is realized by means of an active switching within the refrigerant circuit, having a primary circuit and a secondary section formed from two flow pathways. The configuration of the refrigerant circuit with switching valves, however, leads to great complexity, which in turn causes high costs and great technical expense.
French Pat. Appl. Pub. No. FR 2 743 027 A1 shows a vehicle air conditioning system with a traditional refrigerant circuit, having only an evaporator, a compressor, a condenser, and an expansion element. The heat exchangers are arranged in separate flow channels, fashioned to be separate from each other at least by flow engineering. The flow channels have cross connections of bypasses. The air mass flows taken in by means of fans are conducted across the surfaces of the heat exchangers by closing and opening of valves, as well as conducting through the bypasses as needed and according to the operating mode. In this process, the air mass flows are cooled and/or dehumidified, or heated, and then taken into the passenger compartment and/or the outside.
Thus, air conditioning systems for vehicles are known in the prior art for a combined refrigerator and heat pump operation for heating, cooling and dehumidifying the air being conditioned and taken to the passenger compartment. The air conditioning systems are controlled either on the refrigerant circuit or the air side.
However, with air conditioning systems controlled on the air side, no operation in reheat mode is possible. In turn, the air conditioning systems designed for an additional reheat mode have a more complicated refrigerant circuit with a plurality of components, such as heat exchangers, switching valves, and expansion valves.
In the “reheat mode,” the air taken to the passenger compartment is cooled and thus dehumidified, then the dehumidified air is slightly heated. In this operating mode, the required reheat power is usually less than the required cooling power for cooling and dehumidifying the air.